Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $202.59   5.614%   $213.9634   $213.96   $213.95   $214.00  
  Purchase #2 $29.54   4.636%   $30.9095   $30.91   $30.90   $30.90  
  Purchase #3 $85.78   8.301%   $92.9006   $92.90   $92.90   $92.90  
  Purchase #4 $144.73   12.425%   $162.7127   $162.71   $162.70   $162.70  
  Purchase #5 $233.77   7.828%   $252.0695   $252.07   $252.05   $252.10  
  Purchase #6 $165.45   8.351%   $179.2667   $179.27   $179.25   $179.30  
  Purchase #7 $9.53   6.542%   $10.1535   $10.15   $10.15   $10.20  
  7 purchase totals = $871.39       $941.9759   $941.97   $941.90   $942.10